The present invention relates to d.c. to a.c. inverters and more particularly to such inverter which provides a sine wave output waveform.
In certain circumstances, it is desirable to be able to operate a.c. type loads from a source of d.c. power, such as batteries. For example, it may be highly desirable to maintain the operation of various medical devices during failures of the normal supply power distribution system. For this purpose, various rotary and static inverter systems have been heretofore proposed, including designs employing semiconductor switching components.
As is understood by those skilled in the art, most semiconductor or solid state inverters utilize simple square wave switching. While some loads can be driven from such waveforms, others cannot. While various sine wave inverter designs have also been proposed, these typically have not been usable with a wide variety of loads, particularly loads which exhibit low power factors or which draw current unequally from the two halves of the sinusoidal waveform. Further, most sine wave inverter designs proposed heretofore are relatively expensive and complex or produce only a rough approximation of a sine wave and are thus not suitable for all loads.
Among the several objects of the present invention may be noted the provision of a d.c. to a.c. inverter which provides a sine wave output waveform; the provision of such an inverter which will accommodate loads exhibiting a wide range of power factors; the provision of such inverter which will tolerate loads of drawing unequal current from the different phases of the sine wave output voltage; the provision of such an inverter which provides a sine wave output of high accuracy; the provision of such an inverter whose output voltage is highly regulated against variations in both d.c. supply voltage and variation in load; the provision of such an inverter whose operating efficiency is very high; the provision of such an inverter which is of relatively simple and inexpensive construction and which is highly reliable. Other objects and features will be in part apparent and in part pointed out hereinafter.